feat: implement user data schema and API endpoints

- Add Alembic migration setup with async configuration
- Create 16 user data models (users, decks, cards, replays, etc.)
- Implement comprehensive API endpoints with JWT auth
- Add replay, card collection, group, network, preferences, and activity log routers
- Include API documentation and migration test plan
- Update Dockerfile to run migrations on startup

backend/alembic/env.py

@@ -0,0 +1,86 @@
+"""
+Alembic environment configuration for async SQLAlchemy.
+
+Supports async database operations for migrations.
+"""
+import asyncio
+from logging.config import fileConfig
+from sqlalchemy import pool
+from sqlalchemy.engine import Connection
+from sqlalchemy.ext.asyncio import async_engine_from_config
+
+from alembic import context
+
+# Import all models so Alembic can detect changes
+from app.core.database import Base
+from app.models import (
+    User, DecklistFile, DecklistFolder, Room, RoomGameType,
+    Ban, GameLog, AuditLog, MtgCardMirror, DeckCardLink
+)
+# Import new models
+from app.models.user_data import (
+    UserSession, DeckVersion, GameReplay, ReplayPlayer,
+    GameOutcome, UserStatistics, UserCardCollection, CardWishlist,
+    UserGroup, GroupMember, GroupChatMessage, UserNetwork,
+    NetworkMember, UserPreference, UserActivityLog
+)
+
+# this is the Alembic Config object
+config = context.config
+
+# Interpret the config file for Python logging.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+    
+    This configures the context with just a URL
+    and not an Engine instance though.
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection: Connection) -> None:
+    """Run migrations with proper async context."""
+    context.configure(connection=connection, target_metadata=target_metadata)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    """Run migrations in 'online' mode with async engine."""
+    connectable = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        options={"pool_pre_ping": True},
+        class_=pool.NullPool,
+    )
+
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+
+    await connectable.dispose()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode."""
+    asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()